The present invention is directed generally to electronic pressure transducers, and more particularly to temperature-compensated capacitive pressure transducers having a high degree of linearity.
Electronic capacitive pressure transducers are utilized in a wide range of applications for providing an electrical output signal indicative of a sensed pressure level. Typically, such transducers utilize a pressure sensor element, such as described in U.S. Pat. Nos. 4,178,621 to Simonelic et al., 4,204,244 to Ho and 4,225,632 to Ho, all assigned to the same assignee as the present invention. In these elements the spacing between two spaced-apart capacitor plates is changed with applied pressure, causing a change in the electrical capacitance of the element. An associated processing circuit such as described in U.S. Pat. Nos. 4,250,452 to Gray et al. and 4,392,382 to Myers, which are also assigned to the present assignee, generates an output signal, typically in analog form, from the change in electrical capacitance.
With the advent of computer controlled combustion engines, pressure transducers have come into use for sensing engine manifold pressure, and for providing a signal indicative of the sensed pressure to an engine control computer. Because of the wide temperature and pressure ranges encountered in such engine control environments, and the necessity of restricting the output signal to a relatively narrow range compatible with the computer, it is necessary that the processing circuitry incorporated in pressure transducers utilized in engine control applications have a high degree of linearity, and be substantially unaffected by extreme temperature changes in the operating environment. Furthermore, it is desirable that such transducers be capable of economical high volume production so as to not unnecessarily increase the cost of the engine control system. In particular, because of variations in sensitivity brought about by manufacturing tolerances encountered in capacitive pressure sensing elements, it is desirable that the processing circuitry of pressure transducers in engine control applications be capable of accommodating a wide range of pressure sensor sensitivities.
The present invention is directed to an electronic pressure transducer which provides improved linearity and temperature independence, and which accommodates a wide range of pressure sensing element sensitivities.